The present invention is an outgrowth of the development of an air pallet using low pressure, low cfm air flow exemplified by U.S. Pat. No. 3,948,344 entitled "LOW COST PLANAR AIR PALLET MATERIAL HANDLING SYSTEM", issued Apr. 6, 1976, and U.S. Pat. No. 4,272,856 entitled "DISPOSABLE AIR-BEARING PATIENT MOVER AND VALVE EMPLOYED THEREIN", issued Jun. 16, 1981 Planar air pallets and air-bearing patient movers of such type employ at least a thin, flexible bottom sheet for partially defining a plenum chamber, with said one sheet being perforated by way of small, closely spaced pinholes over a surface area defined by the imprint of the load, which pinholes face an underlying fixed, generally planar support surface. The pinholes open unrestrictedly to the interior of the plenum chamber and to the planar support surface. When the plenum chamber is pressurized by low pressure air, initially the air jacks the load upwardly above the thin, flexible sheet, then air escapes under pressure through the minute pinholes and creates a frictionless air bearing of relatively small height between the underlying support surface and the bottom of the perforated flexible sheet.
In all air pallets, including patient movers, it is necessary to provide controlled pillowing of the thin, flexible sheet material, particularly outside the perforated surface area of that sheet to initially jack the load above the flexible sheet prior to the creation of the frictionless air bearing and to insure the ability of the air pallet to ride over surface projections on the underlying support surface. Means must also be provided within the air pallet to prevent ballooning of the thin, flexible sheet or flexible sheets defining the plenum chamber whereby the plenum chamber takes a circular or near circular vertical cross section, the result of which could be the tilting or rolling of the load off the top of the air pallet. Further, when the load rests on the air pallet, prior to the pressurization of the plenum chamber the load tends to press the perforated flexible sheet into contact with the underlying support surface which prevents the entry of air under light pressure into the plenum chamber. Thus, air dispersion means are required either interiorally or exteriorally of the plenum chamber to ensure pressurization of the plenum chamber.
Under certain circumstances, the load may additionally constitute a generally rigid, i.e., semi-rigid backing member. A cardboard box filled with material for transport may have the planar bottom functioning as a generally rigid backing member. Where the air pallet is formed essentially of a thin, flexible sheet material, a bag of grain acting as the load may constitute a generally rigid backing member.
In the development of the air pallets, and in particular air bearing patient movers as a form of such air pallets as exemplified by U.S. Pat. No. 3,948,344, a corrugated sheet such as sheet 34 within the single chamber functioning as a plenum chamber in a patient mover formed by two superimposed thin, flexible sheets 12, 14 in U.S. Pat. No. 4,272,856 may constitute both a unitary air dispersion means and a semi-rigid backing member (if needed). The semi-rigid backing member may comprise a semi-rigid sheet inserted within a cavity formed between the top thin, flexible sheet and an intermediate thin, flexible sheet. Alternatively, the backing member may be formed of a series of transversely linked air pressurized tubes formed by sealing off parallel, laterally adjacent longitudinal sections of the top sheet and the intermediate sheet. Such tubes may be completely sealed and air pressurized through valves. In a flow-through system, the pressurized air forming the air bearing passes first through parallel, transversely linked tubes defined by the top and intermediate sheets and then into the plenum chamber defined by the intermediate sheet and the bottom sheet with the bottom sheet bearing the pattern of perforations over the foot print of the load. U.S. Pat. No. 4,528,704 issued to Jack Wegener and Raynor D. Johnson, on Jul. 16, 1985 and entitled "SEMI-RIGID AIR PALLET TYPE PATIENT MOVER" is directed to such air pallets.
Flow-through chambers connected by succeedingly smaller sized ports within horizontally extending vertically spaced walls define a series of stacked chambers in a gas pressurized jacking structure and an air pallet including such jacking structure and forms the subject matter of U.S. Pat. No. 4,417,639 issued to Jack Wegener on Nov. 29, 1983 and entitled "DYNAMIC GAS PRESSURIZED JACKING STRUCTURE WITH IMPROVED LOAD STABILITY AND AIR PALLET EMPLOYING SAME". Further, as evidenced in FIG. 10 thereof, such jacking structure may be formed totally of thin, flexible sheet material with vertically separated chambers in communication via a gas passage whose cross-sectional area is smaller than that of the air inlet to the upper chamber thereof through the air inlet hose.
In the semi-rigid air pallet type patient mover of U.S. Pat. No. 4,686,719 entitled "SEMI-RIGID AIR PALLET TYPE PATIENT MOVER", U-straps are sewn to the lateral sides of the patient mover structure for facilitating lateral shifting of the patient placed thereon with the plenum chamber gas pressurized and a thin air film underlying the perforated area of the thin, flexible bottom sheet. The patient may be bound to the top of the patient mover via a pair of crossed VELCRO hook and loop material covered straps for ease in engagement and disengagement of the strap ends about the patient.
In the field of air pallets and particularly of the patient mover type those patient movers formed of multiple, thermal bonded or stitched sheets of thin, flexible sheet material which incorporate a rigid or a semi-rigid sheet as the load backing member are not universally employed in health care treatment facilities. The existence of the rigid or semi-rigid sheet carried within a pocket or cavity defined by two thin, flexible sheets renders the assembly bulky, and adds considerably to the weight of the same. While such patient mover may perform extremely well at a certain hospital station or treatment area such as facilitating patient movement onto and from an X-ray table, the patient mover remains at the area and is unlikely to be employed in moving the patient to and from the hospital bed remote from the X-ray area since hospital personnel resist transporting such patient mover from location to location.
The same is true where the air pallets such as patient movers are utilized by paramedics, shock trauma units or the like. As a result, recently there has been shown considerable interest in the development of soft pad or hard pad air chamber-type air pallets as patient movers or as patient positioners devoid of such rigid or semi-rigid sheet. In the health care field, particularly, the person transported or changed in position in many cases is not truly a patient recovering from sickness, but one requiring continuous attention, such as an invalid or partial invalid. In this case, upon either transport, or positioning and maintaining the patient comfortable in a given partially upright or supine position, the possibility of a tissue breakdown exists with the need for inducing therapy during the time that the patient remains in such given positions for a significant period of time. Essentially, there exists the need for the prevention of skin breakdown which can occur within a very short time whether the patient is in a health care facility or hospital, even while on the operating table of such hospital.
The applicants have determined that there are significant differences between the rigid back air pallet and the flexible or air chamber-type air pallet with a load that can flex. In the development of air pallets and air pallet-type patient movers utilizing a thin, flexible bottom sheet partially defining a plenum chamber and being perforated by way of thousands of small, closely spaced pinholes over the surface area defined by the imprint of the load and which open unrestrictedly to the interior or the plenum chamber and to an underlying planar support surface, such air pallets and air pallet-type patient movers have generally employed a rigid backing member starting with U.S. Pat. No. 3,948,344. Exceptions lie in the patient mover of U.S. Pat. No. 4,272,856, and in the patient mover illustrated in FIGS. 4 and 5 of U.S. Pat. No. 4,528,704.
Certain structural features and parameters with respect thereto play a very important part in the successful operation of an air pallet having a rigid backing member. The key for successful movement of a load on a developed air film by air escape from the perforations is to make the air work on the load and to control the action of the air in doing that job. By matching the footprint of the load to that of the plenum chamber pattern area of perforations, thus generally matching the area of the developed air film to that of the load, the air pallet with the plenum chamber pressurized will jack the load, create the air bearing and permit the load to be stably moved on the air pallet.
If the mass of the load is spread through too small an area against the plenum chamber, i.e., point loading, the load may ground out that portion of the plenum chamber between the load and the underlying planar support surface causing the thin, flexible sheet to bulge out around the point load application against the top of the plenum chamber. Thus, with the plenum chamber up and about the sides of the load, the load is not lifted, the air does not escape through the perforations and no effective air bearing is created. When the load footprint is less than the plenum chamber air film footprint, a significantly greater pressure is needed to lift the load.
Successful operation of rigid backing surface type air pallets requires controlled jacking, controlled pillowing and anti-ballooning. Control of load distribution may be achieved by the use of a rigid backing member such as a board or sheet as part of the plenum chamber, or within a separate chamber supporting the load but overlying the plenum chamber. The rigid backing member distributes the load mass balanced equally over the area of the plenum chamber footprint. The control of the plenum chamber can be performed in several ways and a properly designed plenum chamber can effect several of the control functions, i.e., jacking, pillowing and ballooning.
The term "jacking" covers the act of raising the load so that air can enter into and be distributed throughout a plenum chamber, or multiple plenum chambers, and then pass out through the perforations to form the air film or air bearing while permitting the planar rigid backing surface to support the load and allow it to move on the film of air.
The term "pillowing" describes the ability of the thin, flexible sheet to deform so as to ride over or under surface irregularities in the generally planar support surface (ground, floor, etc.) without bottoming out. If the compressed air within the plenum chamber does not jack the load high enough, the rigid backing member will ground out against the thin, flexible bottom sheet and the surface irregularity (vertical projection).
The term "ballooning" describes the situation where the load is jacked or raised up so high that the load becomes unbalanced on the footprint formed by the plenum chamber. This is normally caused by the thin, flexible sheet tending to become hemispherical (where a generally rigid planar backing member acts in conjunction with the thin, flexible bottom sheet bearing the perforations to form the plenum chamber). The hemispherical configuration given to the thin, flexible bottom sheet permits it to roll about the curved surface tilting to the extent where the load may be dislodged. As may be appreciated, the pillowing control functions as an anti-ballooning means. Absent the generally rigid planar backing member, where the plenum chamber is formed of thin, flexible sheet material such as a bag, the bag will take a circular cross-section when fully pressurized, the true essence of a balloon.
Where the thin, flexible bottom sheet is tightly connected at opposite sides to the generally rigid backing member that rigid backing member functions to control jacking, pillowing and ballooning. Where the rigid backing member is smaller than the thin, flexible bottom sheet, slack develops within the thin, flexible bottom sheet which increases the pillowing capability of the thin, flexible bottom sheet. Excessive slack leads to ballooning.
Other means have been provided for controlling pillowing, such as the lamination of additional members to a center sheet or to either the upper thin, flexible sheet or the bottom thin, flexible sheet. The addition of internal strips lying diagonally from corner to corner within the plenum chamber or vertical from face to face, control the degree of pillowing. The load itself may act as a pillowing control means. The insertion of a rigid plate internally within a thin, flexible bag acts both as a rigid backing member, a pillowing control means and, under certain conditions, an air distribution means for insuring air pressurization of the plenum chamber with the air pallet formed principally by the bag supporting the load prior to air pressurization of that plenum chamber. The size of the blower and thus the air pressure developed within the plenum chamber may constitute pillowing control means, as may valving or gating of the air flow system entering the plenum chamber and creating the air bearing, and the stiffness or flexibility of the material used in forming the thin, flexible bottom sheet. The area of the material around the perforation pattern and between that pattern and the rigid backing member is normally the primary pillowing control means for such air pallets. The proximity of the perforation pattern to the outside edge of the plenum chamber, the slack in the plenum chamber and the rigidity of the backing member all constitute aspects of the pillowing control.
In U.S. Pat. No. 4,272,856 for an operative air pallet-type patient mover, pillowing is controlled by having the pattern of perforations extending to the edge of the plenum chamber and the sides of the plenum chamber are purposely designed to match the head and torso of the patient from the shoulders to the hip, where the load mass of the patient is concentrated. Certain parameters with respect to the load, i.e., weight, patient size and load footprint, are matched to the plenum chamber area, otherwise the unit will not work or work poorly.
The Applicants herein ascertained that an air pallet plenum chamber upon pressurization tends to take a shape resulting in lateral reduction of the plenum chamber air film footprint. Since the patient's body is movable and flexes, this creates significant problems. Not only is such load not rigid, but the top flexible sheet is not a rigid member and, indeed nothing structurally is rigid. Further, only the torso and head is supported by the plenum chamber (i.e., jacked up), and the rest of the body (legs, arms, etc.) simply drag along with the air pallet once an air bearing or air film is created by escape of air through the perforations within the thin, flexible bottom sheet. If the patient has a broken limb, this is not a small problem but a catastrophe. Patient loading on the air pallet and removal from the air pallet produces significant problems. Thus, the ability to create a patient mover having a size to fit the patient, the bed, the portable gurney and a procedure table such as an operating table was quite desirable.
These problems led initially to developments exemplified by U.S. Pat. Nos. 4,528,704 and 4,686,719. However, these developments raised more questions than they provided answers. The key to solving most of the problem areas seemed to lie in the utilization of a rigid backing member, but a rigid backing member made it more difficult to place the patient on the patient mover. The patient has to be physically log-rolled way over, and almost face down to one side so that the rigid backing member is juxtapositioned to the patient, and the patient is then rolled back over so that the patient ends up supine on the patient mover. This procedure follows that of placing the sheet under a patient when on a hospital bed, but than a sheet can be folded in half and slid under the patient without turning his body excessively to one side. Such is not so for a patient mover having a rigid backing member.
Attempts were made for formulating a useful air chamber-type air pallet using a flexible pad to eliminate the rigid backing member. Generally at the same time, the applicants considered the separation of the jacking action from that of creation of the frictionless air film. This led to the development of stacked tubes, one functioning as a pure jacking chamber, and the second as a combined jacking chamber and plenum chamber. The result is a gas pressurized jacking structure with improved load stability, in which the same compressed air pressurizing the upper chamber through a dynamic flowthrough arrangement, functions in passing through the pin hole perforations of the plenum chamber thin, flexible bottom sheet, to create the air film.
In air chamber-type air patient movers, a phenomenon was experienced as the result of air pressurization of the tubular chambers formed by sealed sections of the upper two thin, flexible sheets and the air pressurization of the plenum chamber underlying all of the upper row of tubes common to the intermediate thin, flexible sheet of said row of tubes. The entire unit took on a full vertical circular cross-section and attempted to approach a cylinder, which was termed "hot dogging". During hot dogging, the plenum chamber takes on an almost circular cross-section in a plane at right angles to the longitudinal axis of the series of joined tubes formed by the top thin, flexible sheet, the intermediate thin, flexible sheet and the bottom thin, flexible sheet of the air pallet. A plenum chamber is formed between the thin, flexible intermediate sheet and bottom sheet with the bottom sheet having literally thousands of closely spaced pinholes through which air escapes from the plenum chamber to form an air film or air bearing A between the thin, flexible bottom sheet and the generally rigid, planar surface beneath. Each of the transverse seal lines joining the top and intermediate sheets, which together form individual air pressurizable chambers or tubes, function as hinging areas between adjacent tubes. The result of such hinging is the high instability for any load in contact with the exterior of the top thin, flexible sheet. It is further obvious that the single large sectional area formed by the plenum chamber is without a means for controlling hot dogging and is thus extremely susceptible to this instability problem.
A stable, useful air chamber-type air pallet is further hampered by a phenomenon resulting both in an instability problem and, under severe conditions, a loss or reduction in effective plenum chamber air film or air bearing footprint area to the extent where the air bearing cross-sectional area becomes too small to carry the load, the load may roll off the upper flexible sheet support area as the air pallet assumes a cylindrical shape and the air pallet may ground out as it loses air bearing cross-sectional area, or a combination of all three adverse effects occur.
Another phenomenon which occurs utilizing air chamber-type air pallets is a lack of rigidity of the air chamber assembly defined by the top thin, flexible sheet and the intermediate thin, flexible sheet as a result of air pressurization of all of the chambers of the row of tubes and the air pressurization of the plenum chamber, which underlies the tube array defined by the top and intermediate thin, flexible sheets. While the walls of the individual chambers or tubes are relatively taut, upon air pressurization, the line connections between abutting sides of the parallel row tubes permit tube sectioning lines to act as hinges which cause the unwanted hot dogging of the air pallet. The presence of a load such as a patient and the weight of said patient depressing the upper surface of the air pallet tends to resist the ballooning of the air pallet and enhance the stability of the load. However, such structures inherently lack means for preventing significant lateral shrinking of the plenum chamber.
In view of the lack of rigidity of early air chamber-type air pallets, an investigation of the various causes for suppleness in contrast to desired rigidity (by attempting to substitute an air chamber or chambers for the rigid backing member) led to the determination that rigidity of any part of an air chamber-type air pallet can be achieved from solely two means: varying the air pressure within the various chambers of the air pallet (the result of which tends to create ballooning with the high air pressure found to be undesirable due to the ballooning) and employing a solid unbendable stiff upper sheet supporting the load which, for a point load, spreads such load over the complete surface of the unbendable upper sheet. While the unbendable upper sheet was sufficient to provide rigidity and avoid ballooning in one embodiment of U.S. Pat. No. 4,528,704, the necessary rigidity can only come from the air pressure within, or flowing through, the various chambers of the thin, flexible sheet structure in the embodiment disclosed in FIGS. 4 and 5 of said patent.
In operation of air chamber-type air pallets of the design of U.S. Pat. No. 4,528,704, the plenum chamber being unsectionalized and linked solely to the tubular arrays at opposite ends and along opposite sides of the air pallet, such structure either creates, or enhances, suppleness of the structure which prevents the row of tubes of said air pallet from acting as a substitute for the rigid backing member normally employed in such air pallet structures. This results in hinging between the inflated tubes, ballooning of the structure, creating instability.
In U.S. Pat. No. 5,067,189 entitled AIR CHAMBER TYPE PATIENT MOVER AIR PALLET WITH MULTIPLE CONTROL FEATURES, issued Nov. 26, 1991, the foregoing described problems of over pressurization causing instability of the patient mover and the load, enlargement of the underlying plenum chamber to an almost vertical circular cross-section, i.e. "hot dogging", during pressurization, the requirement for a rigid or semi-rigid backing member to prevent "hinging" between individual longitudinal chambers or tubes for supporting the load, and the point load grounding out on the underlying support surface due to load shifting were tentatively resolved. During the course of improving the earlier air pallet patient movers of the air chamber type, it was found that all of the recited problems with prior types of inflatable air pallets were substantially interrelated, as well as the discovery of an additional structural problem described as the reduction or shrinkage of the lateral dimension of the air pallet. U.S. Pat. No. 5,067,189 reduces the recited problems through a novel interrelated structure. In lieu of a rigid or semi-rigid backing member, a series of stacked rows of pressurized chambers or tubes have been utilized which create a pre-determined air dispersion which, in concert with the air dispersion in the underlying plenum chamber, properly jacks the load, e.g. a patient, and maintains the flexible backing surface (the stacked rows of tubes or chambers) in a planar direction generally parallel to the underlying developed air film. Simultaneously, the plenum chamber is inflated and through the underlying perforations creates an air film between the air pallet and the fixed support surface, but only in an area which generally matches the footprint of the load. Further, the inflation of the plenum chamber within the parameters set forth in U.S. Pat. No. 5,067,189 creates a sufficient pillowing means to permit the air pallet to accommodate surface irregularities and move the load on the developed air film without bottoming out and without the bottom flexible sheet ballooning outward. This is accomplished through a series of vertical and oblique ties which restrain the separation of an intermediate sheet forming the bottom of the linked rows of chambers or tubes and the underlying bottom sheet of the plenum chamber from moving outward one from the other beyond a pre-determined distance. These ties (or stringers) in combination with the stacked rows of chambers or tubes prevent "hot dogging" of the air pallet when inflated, tend to reduce lateral shrinkage of the air pallet because of its anti-hot dogging and anti-ballooning effect, and increase the ability of the air pallet to accommodate surface irregularities when in motion so as not to create a point load problem, all of which increase the load stability of the particular air pallet.
The present invention takes the ongoing development process for the air chamber-type air pallet capable of patient movement to a higher degree of functionality and support without seriously disrupting the continued treatment of a patient. Because the linked array of inflatable air chambers or tubes of U.S. Pat. No. 5,067,189 were longitudinal in direction, the ability to bend or fold the air pallet and continue to support the load once inflated was substantially negated. It was also determined that proper positioning of the patient (the load) centrally on the longitudinal center line of the air pallet was critical in preventing rotational instability. These noted deficiencies, as well as the retention of certain of the described stability requirements, have now been incorporated in an improved air pallet capable of patient movement and treatment.